1. Field of the Invention
The present invention relates to an injection quantity control unit that controls injection quantities of fuel injection valves, which inject fuel into corresponding cylinders of a multi-cylinder internal combustion engine, and a fuel injection system having the unit.
2. Description of Related Art
Conventionally, in a fuel injection system, in which fuel is injected into each cylinder of a multi cylinder internal combustion engine by corresponding one of fuel injection valves, a variation amount of a rotational speed in an explosion stroke varies among the cylinders because of the variation in injection quantity of the fuel injection valve due to, for example, manufacturing errors in manufacturing the valves. Accordingly, engine vibration may be generated due to variation in the rotational speed variations. For example, when the rotational speed variations of the cylinders vary in an idle operational state and thereby the engine vibration is generated, the engine vibration may cause discomfort to a vehicle occupant.
In order to reduce such variation in the rotational speed variations among the cylinders, an inter-cylinder injection quantity correction, whereby the injection quantities of the fuel injection valves which inject fuel are corrected for respective cylinders, is known (see, e.g., JP3591428B2). In the conventional inter-cylinder injection quantity correction in JP3591428B2, the injection quantity of the fuel injection valve is corrected based on the rotational speed variation in the explosion stroke of each cylinder, to reduce the variation in the rotational speed variations among the cylinders. For example, in a cylinder with a large rotational speed variation, the injection quantity of the fuel injection valve is reduced, and in a cylinder with a small rotational speed variation, the injection quantity of the fuel injection valve is increased.
However, the rotational speed variation, which is a difference between the maximal value of the rotational speed in the explosion stroke of each cylinder and the minimum valve of the rotational speed at the start of the explosion stroke, is influenced not only by the injection quantity of fuel injected into each cylinder in the explosion stroke but also by the rotational speed variation of an immediately preceding cylinder which performs the explosion stroke immediately before each cylinder.
Each cylinder tends to rotate an internal combustion engine against the moment of inertia of a piston in the immediately preceding cylinder at the start of the explosion stroke. As a result, if the fuel injection quantity is the same, when the rotational speed variation of the immediately preceding cylinder is small and the moment of inertia of the immediately preceding cylinder becomes small, the rotational speed variation of each cylinder becomes large, and conversely, when the rotational speed variation of the immediately preceding cylinder is large and the moment of inertia of the immediately preceding cylinder becomes large, the rotational speed variation of each cylinder becomes small.
When the injection quantity is corrected in the above manner based on the rotational speed variation of each cylinder increased or decreased because of the influence of the rotational speed variation of the immediately preceding cylinder, the injection quantity cannot be corrected with high precision to reduce the variation in the rotational speed variations among the cylinders. Consequently, when the variation in the rotational speed variations among the cylinders is especially large, a period taken to reduce the variation in the rotational speed variations becomes long.